Abstract: 8-Bromo-4′ 7-dihydroxy isoflavone(Ⅴ) was synthesized from 2-bromorecercinol (Ⅱ).Debromonation occurs unexpectedly by using BF₃-ether as Lewis acid in F.Creaction between Ⅱ and p-methoxy-phenylacetic acid.Demethoxylation of 3-brpmo-2,4-dihydroxy,4′-methpxy .deoxybenzoin(Ⅲ) was carried out in CH₃CN at - 10℃ with excess of BBr₃ (1:10mol).3-bromd-2,4,4′-trihydroxydeoxybenzoih(Ⅳ) was cyclized with N,N-dimethyl formamide dimethyl acetal to give Ⅴ,and a by product, 4′,7-dimethoxyisoflavone, was also isolated, Ⅳ was also prepared by the direct bromination of 2,4,4′ -trihydroxydepxybenzoin.